Teenagers do not need to be rail thin to be practicing the dangerous eating behaviours associated with anorexia, a new study suggests.

Rather, the true measure of trouble may be significant weight loss, and the Australian researchers noted that a drastic drop in weight carries the same risk for life-threatening medical problems even if the patient is a normal weight.

Even more concerning, the scientists saw a nearly six fold increase in this type of patient during the six-year study period.

Anorexia nervosa

Anorexia nervosa is a mental illness characterised by excessive weight loss and psychological symptoms that include a distorted self-image and fear of weight gain. In some patients, this can also include depression and anxiety. Those who have these symptoms but are not underweight enough to qualify for the definition of anorexia fall under a different diagnosis, known as Eating Disorder Not Otherwise Specified (EDNOS-Wt).

"Emaciated bodies are the typical image portrayed in the media of patients with restricting eating disorders such as anorexia nervosa," said lead researcher Melissa Whitelaw, a clinical specialist dietician at The Royal Children's Hospital in Melbourne, Australia. "This paper highlights that it is not so much about the weight but the weight loss that can lead to a serious eating disorder. The complications of malnutrition can occur at any weight."

In her study, which included 99 teens aged 12 to 19, Whitelaw found only 8 percent of the patients had EDNOS-Wt in 2005, but more than 47 percent of the patients had it in 2009.

"I was surprised to see how much it increased," Whitelaw said. "I was also surprised at how similar they were not only physically but also psychologically. Everything about them was anorexia except that they don't look really skinny." Both groups had even lost a similar amount of weight: a median 28 pounds for those with anorexia and 29 pounds for those with EDNOS-Wt.

Spotting eating disorders

Other experts noted that it can be difficult to spot this less obvious eating disorder.

"We are conditioned to think that the key feature of anorexia nervosa is low body mass index [BMI]," said Cynthia Bulik, director of the Centre of Excellence for Eating Disorders at the University of North Carolina at Chapel Hill. BMI measures whether a person is a healthy weight for their height.

"In fact, we miss a lot of eating disorders when focusing primarily on weight," Bulik added.

Leslie Sim, an assistant professor of psychology at Mayo Clinic Children's Centre in Rochester, Minnesota, said, "People are calling it atypical anorexia, but we see it every day. We see people who have all the psychological, behavioural, cognitive and physical symptoms of anorexia nervosa, but the only difference is their weight."

In this study, the side effects of having an eating disorder were also very similar. Dangerously low phosphate levels occurred in 41 percent of anorexia patients and 39 percent of EDNOS-Wt patients. The lowest pulse for the teens was 45 beats per minute (bpm) for those with anorexia and 47 bpm for the other group. Meanwhile, 38 percent of the EDNOS-Wt patients and 30 percent of the anorexia patients required tube feeding.

"[Normal-weight patients with anorexia symptoms] were becoming medically unstable, despite the fact that they had what you would call a normal body weight," Whitelaw said.

Unclear reasoning

The reasons for the apparent increase in these patients is less clear, but both Sim and Whitelaw said it is likely a combination of increased awareness of the problem and an increased focus on obesity. One tricky aspect of identifying these patients, Sim said, is that the weight loss appears at first to be a positive development.

"These patients just fly under the radar and when they're in that earlier stage, it's harder for people to see it," Sim said. "Parents say to me every day, 'I thought my daughter was doing something good and making healthy choices until it got out of control. We didn't know it was a problem until she couldn't eat the cake at her birthday party.' "

The experts emphasised that eating disorders are not parents' fault. Instead, parents can play an important role in identifying the symptoms of an eating disorder, especially in its early stages, said Jessica Feldman, a licensed social worker and site director of The Renfrew Centre in Radnor, Pennsylvania. Symptoms include significant changes in eating patterns, excessive exercising, a teen's negative statements about their body image, an increase in depression or anxiety, and a loss of interest in previously enjoyable activities.

Bulik stressed the importance of recognising that both conditions are illnesses.

"No one chooses to have an illness. We would never tell someone with allergies to 'just stop sneezing'," Bulik said. "Although dieting might be a first step, the illness takes over and develops a life of its own – sufferers often cannot eat, even if they want to."

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